Coring subterranean formations



Dec. 1, 1959 F. H. DElLY 2,915,285

CORING SUBTERRANEAN FORMATIONS Filed May 23, 1956 3 Sheets-Sheet 1 AMW 34 33 FIGURE I Fredric H. Deily Inventor Y 7 Attorney Dec. 1, 1959 F. H. DEILY some SUBTERRANEAN FORMATIONS 3 Sheets-Sheet 2 Filed May 23, 1956 3 6 I Y o Q m a Y H MGM I Tm 6 MA WAR, Wu m wm X A Wu F- Q m S O P s m C LATCHING D063 FIGURE 2 In ventor Fredric H. DeiIy Dec. 1, 1959 F. H. DElLY CORING SUBTERRANEAN FORMATIONS Filed May 23. 1956 3 Sheets-Sheet 3 United States Patent-O Fredric H. Deily, Tulsa, Okla assignor, by mesne assignments, to Jersey Production Research Company Application May 23, 1956, Serial No. 586,724

8 Claims. (Cl. 2551.4)

The present invention broadly relates to the coring of subterranean formations. More particularly, it concerns an apparatus and method of coring a subterranean formation wherein the resulting core is chilled as it is cut and its true fluid content thereby maintained. The invention .has particular application in coring subterranean oil reservoirs prior to secondary recovery operations.v

The importance and desirability of obtaining cores that are truly representative of subterranean formations have long been recognized in the petroleum industry. A study of these cores provides the industry with knowledge which enables production operations to be carried out with maximum efiiciency and economy. The analysis and study of core samples is becoming particularly important in those reservoirs and fields which are being considered for secondary recovery operations. The permeability, porosity, grain orientation and other characteristics of the cores provide prospective operators of the reservoir with extremely desirable information concerning the direction and rate at which a reservoir should be depleted as well as the type of secondary recovery technique which should preferably be employed.

Accordingly, it is an object of the present invention to provide an improved method and apparatus for coring subterranean formations and especially subterranean oil reservoirs that are being studied preparatory to secondary recovery programs. Briefly, the invention utilizes a stream of gasiform fluid which is expanded and caused to perform work in the vicinity of a coring tool. Thus, a stream of high pressure air may be employed to drive a gas turbine located near the bottom of a bore hole, and the gas turbine in turn employed to drive a coring tool. The stream of high pressure air in passing through the turbine is expanded rapidly and experiences a sudden 'and severe temperature reduction. The chilled, low-pressure air stream is then'directed around the core which is cut by the coring tool; and the core is thereby chilled,

degree of chilling, a suitable energy dissipation device may also be provided near the bottom of a bore hole to be actuated by the turbine. In this manner it is possible to thoroughly chill or freeze a core sample immediately as it is cut from a subterranean formation, independent of the amount of work which is actually required to do the cutting. The frozen core may be then lifted to the surface of the earth and further chilled and analyzed or studied as desired.

The nature and scope of the present invention may be better understood by reference to the attached drawing in which Figure 1 illustrates in vertical cross section an drill pipe.

'50 to degrees F. at the surface.

'ice

Figure 2 illustrates schematicallythe apparatus of Fig ure 1 as it may be adapted for use in a wire line type of operation. v

Figure 3 illustrates in greater detail a latching apparatus suitable for use in the apparatus of Figure 2. 1

Referring to Figure ,1, there are illustrated therein'a bore hole 10, drill pipe 11, housing 12, bypass conduit 13, air chamber 14, magnetic brake 15, brake shaft 16, turbine rotor 17, coring drive shaft 18, outer core barrel 19, inner core barrel 20 and bit 21.

Drill pipe 11 extends to the topof bore hole 10 and is secured rigidly torsionally tosuit'able torqueresisting apparatus, not shown, such as a conventional rotary table. Also not illustrated in Figure 1 is surface apparatus for furnishing a supply of compressed and cooled air to the string of drill pipe. It will be recognized, however, that conventional air compressors may be emplo yedto compress atmospheric air, and that conventional heat exchangers or other coolers may be used to cool the compressed air to a desired and suitable temperature for down hole use. For the purposes of the invention, it is generally desirable to employ air having a pressure of from about 600 to 900 p.s.i.a. and a temperature of about Furthermore, with air of this pressure and temperature, it is contemplated air rates of about 600 to 1200 standard c.f.m. are sufficient to employ to provide the energy and chilling requirements .of the invention in its application to substantially all coring operations.

Attached to the lowerend of the string of drill pipe is elongated substantially cylindrical housing '12 which contains the energy dissipation device 15 and air chamber 14 as well as the turbine rotor 17. The portion of the housing enclosing the energy dissipation device 15--e.g a magnetic brake-and air chamber 14 is separated from the portion of the housing enclosing the turbine rotor 17 by means of a suitable wall 26. It will be appreciated,

of course, that housing 12 may be a single unitary structure; or, alternatively, it may include separate but interconnectable portions-each portion housing a separate operating component. 1

For the purpose of this description, it will be assumed that the energy-dissipation device 15 is a magnetic brake. As shown schematically in Figure 1, such a brake basically consists of a cylindrical iron fly wheel 6 and a plurality of electromagnets 5. Electrical power for the magnets may be supplied from the surface of the earth as by means of electrical leads 7. The magnets are. electrically excited through these leads; and they create a magnetic flux which permeates the gap and the iron in thecylindrical fly wheel, causing eddy currents to be established. The fly wheel energy is converted into heat by means of these eddy currents, and the heat in turn is dissipated as described below. Pairs of brakes are preferably provided to avoid bending of the shaft 16.

Device 15 is preferably mounted above turbine rotor 17 and is driven from the motor by means ofthe drive shaft 16. Air chamber 14 is preferably positioned vertically intermediate the brake 15 and turbine rotor-17 and is connected directly to the interior of the drill pipe by means of bypass conduit 13. It will be apparent that the dissipation device 15 in the form of amagnetic brake or other suitable means will heat considerably in its operation, thereby making it desirable to bypass the downflowing air stream around this portion of the overall: apparatus. An insulation barrier 22 is therefore preferably provided between bypass conduit 13 and device 15 to minimize heating of downeflowing air prior. to its introduction within the turbine rotor 17. Upper insulated wall 23 and lower insulated wall 24 are'also preferably pro vided to further isolate the device 15 thermally frQmIthe down-flowing air. The housing 12 is perforated or 'prosernbly i.e.,,,the core barrel proper. ports 3:2 are-provided .in Wall .31 to enable exhaust air from the turbine section to fiow to the annular space 33 bore hole. T21 resting'on thehole bottom, high pressure air is transvided with a suitable heat transfer surface 25 to enable heat generated by the action of device 15 to be dissipated into the up-fiowing stream of air in the annular bore hole spacesurrounding. the,drill=pipeand overall drill assembly.

, Suitable; ports 30-. are provided in,.wall 26 to. enable down-flowing air in air chamber 14 to flow to turbine rotor 17. These portsmay be. simple conduits, but-they are preferablynozzles suchas are employed .invarious types of turbines. :Fu'rthermore, turbine rotor, 17.,may be of :1 type which is employed in either impulseor. reaction turbines, although it is preferred that a combined unit, consisting of a double-velocity impulse, or Curtis stage, followed by some reaction stages be used. It will be recognized that the interior surface of the housing 12 .which surrounds turbine rotor 17 may, be: provided. with conventional turbine blading or nozzles and thereby con- ,stitute a conventional turbine stator. As shown in Figure 1,,a, plurality of turbine blades! secured to the housing .1 .;define the turbine stator.

Immediatelybelow the turbine section isa wall 31 which defines the lower portion of housing 12 and which separatesthe turbine section fromthe coring tool as- Suitable exhaust ,between the inner and outer barrels of the core barrel.

The, coring assembly or core barrel includes outer barrel 19, inner barrel 20 and coring bit 21. The bit in this instance is considered tobe a multi-cutter bit, although otherconventionalbits such as diamond bitsand the. like are entirely suitable.

The interior wall surfacepf outer barrel 19 and the outerwall surface of the inner barrel20 define in combination annular space 33 which provides a'flow path for the air which enters the coringtool assembly through the passageways 32. The air exhausting from the lower portion of,the coring tool in the vicinity of the cutter elements contacts the outer surface of the corej34 and 'thencefiows around the cutter elements into the bore hole whence itflows up to the surfaceof the earth.

Suitable bearings 40 are provided around 'thedrive shaft 16 and the coring tool drive shaft 18 to enable these two shafts to turn freely within the housing 12.

These bearings necessarily must be of a character to pro- .vide substantially fluid-tight relationship between these shafts and the surrounding'housing. Swivel joint 41 is provided between outer barrel 19 and inner barrelli] in order that the latter barrel may be free to rotateduring the coring operation relative to the inner barrel. Rotary seals '42 are preferably provided between the outer'barrel 19 and the housing 12 to properly direct the downflowing air stream and to permit relative rotaryrmotion between the outer barrel 19 and the housing 12.

"Having briefly set'forth the apparatus components of directed toward a consideration of the: manner in which this apparatus operates.

For the purpose of this part of the description of the invention, it will be assumed that the apparatus has previously' been assembled and lowered to the bottom of a Withthe cutting elementsofthe coring bit mitted from-the earths'surface down through drll pipe 11 to the interior of the top portion of housing 12. The

"down-flowingairthen' passes through bypass c0nduit'13 into-air chamber 14and thencethrough passageways 30 to the turbine rotor 17. Flow of the airpast the rotor blades and/or nozzles "causes'rotary movement of the turbine rotor and'resulting expansion and temperature reduction of the-air. It will be apparent,-of-course,-that -=the' upper end of the drill-string is'held'stationarypr roof the energy dissipation device (e.g. the rotor portion of magnetic brake 15) as well as the outer barrel 19 of the coring tool.

The exhaust air from the turbine rotor 17 travels through passageways 32 into the annular space between the inner barrel 20 and the outer barrel 19 of the coring tool. The air then flows down the annular space, contacts the core as it is cut by the cutting elements and then'fiows upwardly within the bore hole 10.

Since the exhaust air from the turbine blades has been expanded and therefore chilled by the work it performs on the turbine rotor, it is capable of chilling the core as it is cut to a very low temperature. The up-flowing air within the bore hole, beingv still relatively cool, provides a cooling effectfor the energy dissipation device 15 via the perforations 25 or equivalent heat transfer means. It will be recalled at this point that device 15 is insulated by means of insulating members .23, 22 and 24 from the down-flowing air stream; andzthe coo1ingeflect of. the lip-flowing .air within the borehole isItherefore very desirable in keeping the device at asafe operating temperature.

When a sufficient amount of core has been cut and lodged within the inner core barrel'20, the operation of the turbine and the coring tool may be interrupted; 'the core broken and retained in the core barrel; and themtire assembly removed to the surface of the earth.

.It will be recognized that the size or power ratingof the turbine portion of the apparatus described above will be governed by the size of the coring tool among other factors. For presently conventional operations, it iscontemplated that a turbine producing about 40 horsepower transmitting about 30 horsepower to .the dissipation device and some 10 horsepower to the coring tool will be amply suitable.

It will be recognized at thispoint that numerous modifications ofthe apparatus in Figure 1 maybe employed without departing from the spirit or scope of the invention. For example, energy dissipation devices other than a magnetic brake-egya Prony brakernay be used. Similarly, the entire assembly may be constructed to be lowered inside drill pipe or casing by means'of a wire line in much the same manner as. presently conventional electric drills. Furthermore, the apparatusmay be wireline operated or employed in'a drilling-with-casing' technique. This system, which'hasattractive possibilities; is schematically illustrated in Figure '2 and Figure 3.

Referring'to Figure 2*andFigure' 3, it will be seen that the apparatus in these figures comprises an air compressor 60, heat exchanger 61; auxiliary refrigerationunitfiZ, wire line 50, well pipe or casing 11, retractable gas turbine and coring means 9 and rotary table 63. It will further be seen that theturbine and coring assembly'9 with its attached coring bit 21 is equivalent 'to the apparatus which is illustrated in detail in Figure 1. "In other words, the assembly 9 may be considered to be a structure like that in Figure 1including a housing which embracesan energy dissipation device, an air chamber and a gas turbineand a core barrel which is supported from the housing.

As indicated above, the turbine and coring assembly 9 in Figures 2 and 3 diifers from the apparatus illustrated in Figure 1 primarily in that the former'apparatus is 'of a character to be wire line operated. Thus, referring to Figure 2, it will be seen that the assembly 9 is secured at its upper end to a latching assembly 53 which is adapted to engage the inner surface'of the well pipe 11 when the assembly 9 is lowered to a drilling position within the pipe. The use of a latching assembly for lowering drilling equip- -ment within a string of well pipe and for thereafter retracting the equipment from 'the pipe has been previously "described at'lengthinthe art'e.g., in U.S."Patents" No. 2';330,083-and 2,338,670 and-in pending Usppatentaapplications Serial"No.268',89l (filed January'29,l952) now'PatentNo. 2,764,388, and Serial'No."268 ;894 (also filed January 29, 1952) now Patent No. 2,771,275.. All of these patents and. patent applications generally relate to drilling procedures and apparatus that utilize'retractable bits.. In view of the very complete description of suitable latching. assemblies in these U.S. 'patentsi'and patent applications, it is considered that a lengthy. discussion of such items would be superfluous in the present description. It will be-noted; however, that. any latching assembly 53 will generally include one or more latching dogs 54 which are adapted to engage recesses disposed within the inner surface of the well pipe 11. Furthermore, these recesses are spaced from the lower end of the well pipea distance such that thedrill bit 21 extends beyond the well pipe and engages the bottom'of the bore hole .when the latching dogs are engaged within the recesses.

Conveniently, a shoulder '55 is provided along the inner periphery of the well pipe 11 to support and stabilize the turbine and drill assembly 9 in its drilling position. Furthermore, an annular .seal 56 is preferably provided as indicated to cause down-flowing gas within drill pipe' 11 to flow down through the turbine andsdrill assembly 9. and

. to resist torsional forces that are developed by operation of the assembly 9. Suitable hoisting and lowering equip- 51 shown inFigure 3 is more suited for raising equipment rnent, not shown, is also provided for operating the wire line 50. A packing gland or other suitable blowoutprevention means is preferably provided where wire line 50 passes through the upper termination of the well pipe ll.

'A latching overshot 51.is providedat the lower end of the wire line 50 for engaging the latch or spearhead 52 which is provided at the upper endtof the latching assembly 53.

To aid in understandingthe nature of a latching assembly suitable for the practice of the present invention,

' attention is next directed to Figure 3. This figure shows a latching structure in'greater detail than is 'donein Figure 2. As in Figure 2', the structure in Figure 3 includes wire line 50, turbine and coring means 9, overshot 51, spearhead 52, latching assembly 53, seal 56, latches 54, flange 55 and coring bit 21. All of these components are disposed within a borehole 10 and within the well pipe 11.

Latching assembly 53 comprises an upper body member 80 and a lower body member 83. Upper member 80 has a spearhead 52 at its upper end and a passageway 57 which extends throughout its length. The middle portion of the upper member is reduced in diameter and contains a plurality of circumferentially' spaced ports or "slots 1 82. The lower end of the upper member terminates in a flange 81 which is up-turned at its outer periphery to define a cup-like structure. I

Lower member 83 fits and slides within the passageway 57 of upper member 80 and has at its upper end a plurality of latch pivot supports 84 which extend radially outward throughthe ports 82. A separate latch 54 is secured to .7 each pivot support and is adaptedto engage with the recess in the well pipe.v A centralpassageway 85 extends the length of" the lower member 83 and provides fluid communication between passageway 57 and the upper end of the turbine and core barrel assembly. .'A suitable packer e.g.,.a cup-type packer-is provided o'n lower member 83 and cooperates with the flange 81 of the upper member to effect a fluid-tight seal around the inner surface of the well pipe 11.

The apparatus of Figure 3,it will be noted, is shown in its drilling position with overshot 51 detached from the spearhead 52. It will also be noted that the individual components of the apparatus in Figure 3 may be threaded or otherwise joined together as may be necessary to effect easy assembly and disassembly of the apparatus.

than for lowering it .into drilling position.

To retract the apparatus of Figure'3, the overshot 51 is lowered intoposition over the spearhead 52, whereupon the dogs 88 engage the spearhead. An upward thrust on the wire line then causes uppermember 80 to moveupward relative to the lower member 83. The up-turned portion of the flange 81 causes dogs 54 to be retracted from the recessin pipe 11, and it also releases the load on the packer 90. The apparatus is then free to be lifted and removed from theiborehole.

Having briefly described the apparatus components that are present in Figureg2, attention is now directed toward a, consideration of. thernanner in which the apparatus of this figure may be operated. It will be assumed, for the sake .of convenience, that the hole 10 has been drilled into the earth using a drilling-with-casing technique such as is set forth in the patents and patent applications mentioned earlier in this description. It will further be assumed that the retractable bit used-for drilling the bore hole itself has been removed from the hole and that it is now desired to take a core sample of the formation underlying the hole.

- With these assumptionsin mind, the turbine and drill assembly 9 is; latched to the latching overshot 51 at the surface of the earth; and the assembly is lowered within the well pipe 11 until the, latching dogs 54 engage recesses disposed within the inner wall surface of the well pipe near the bottom of the hole. The latching overshot 51 is then detached from the latch-52, raised at least some distance from the latch andpreferably removed entirely from the borehole. At this point, it will be noted that the overshot There are numerous overshots, however, available for either or both types of operation; and a'detailed description of additional overshots is therefore not, considered to be vital for clear understanding of this invention.

,Air or other gas is then supplied to conduit 70 which in turn conveys the air to the interior of the well pipe. The

air is'conveniently withdrawn from the atmosphere by means of air compressor 60 and pumped via line 64 to heat exchanger 61 where'it is cooled to a predetermined desired temperature. From this point,'the cooled compressed air or other gas is then conveyed bymeans of line 65' to conduit 70 and thence to well pipe 11.

If thecompressed air in line 65 is not at a low enough temperature for desirable operation, at least a part of the compressed air from heat exchanger 61 may be further cooled by passing it through an auxiliary surface refrigeration unit 62. The air issuing from the'latte'r unit is.cornbined with the air in line'65 as desired and thereafter supplied to the drill pipe as by means of conduit 70.

Once within the well pipe 11, the compressed cooled air flows down the pipe and thence through conduit 57 into the turbine and drill assembly 9. Bypassing of the turbine and drill assembly is conveniently prevented as by means .of an annular seal ring 56 as mentioned previously.

Packer 90 is also effective for preventing by-passing.

The compressed air upon entering the assembly 9 serves the same function or functions as were enumerated and described in connection with the apparatus in Figure 1. Thus, the air drives a turbine which in turn simultaneously drives the coring bit 21 and an energy dissipation device.

The latter device, as in the apparatus of Figure 1, 0p eratesto lower the temperature of the air exhausting from the'turbine of assembly 9 to a temperature low enough to chill 'or freeze the core which is cut by the coring bit [21. Exhaust air flowing past the bit escapes from the ,wellby. flowing in anupward direction within the anr '--and suitable surfaceequipment-may be used-to-apply the "desired portion -of the d rill string-weightto the -hole 'bottom.

When a' sufficient core has been cut by the coring bit,

V -A coring apparatus-adapted .tolbe lowered within a estringaof; well pipetand to: be, supported therefrom. which comprises agasepoweredtturbine;andcore barrel assembly, zsaidrassembly including saidturbine and-an energy dissithe core may beparted and retained within the core spationwdevicerconnectedntowanddriven-by.saidturbine,

'barrel in-any conventional-manner. For example, suitable core catchers, with or-without-pressure core barrel facilities may be employed as desired.

Following this, the wireline50 is lowered until the -;saidenergy;:dissipation device being disposed above. said :;turbine: and.;said.core .barrel being disposed below said turbine,;latching ,means. connected to said assemblyand adapted .to; engage latching recesses vdisposed. within. said latching overshot-SIengages-the -latch.52; and the aseavellg.pipe,;.means;.to:supply a,-..strearn of compressedgas sembly-9-may then be Withdrawn fromthe well by pulling upwardlyzon the wire line. The latching dogs 54 are retracted byan-up-ward thrust on thea-wire line, enabling the "latching assembly-and-the= attached turbine and drill assembly to be raised. and removed from the bore hole.

It is apparent from the foregoing description that numerous modifications of the apparatus may be employed --without'-departing' from the spirit or scope of the inven- 1 tion. For example it will-be recognized that other suit- .:t0. said turbine, at coring-bit. supported by said core barrel .and;adapted;;to; .bedriven by. saidqturbine, and conduit means adapted to .transmitexpanded exhaust gas from said 1 turbine ;to. said coring .bit.

e4.. An;' apparatuses defined in clairn' 2 in which the energydissipationdevice is amagnetic brake.

. 5.. A coring-apparatus. adapted to.obtain a core sample 1 from the bottom-ofa bore .holewhich comprises in com- .-:bination a gas-powered type turbine adapted to be lowered able-means for latching or securingihe turbine and core ZOtlWithinihebOIe 11016, 63 t0 Itfansmit a Compressed gas barrel assembly to the inside surface of a Well pipe-may be'used. Furthermore, thelatching means maybe sup- --ported from the-turbine-or other portion of theassembly i rather than constituting a single added feature of the-overall-structure such as is illustrated in the drawing.

I As. pointed outearlier in this description, energy-dissipation devicesof various types may becemployed. Where a particular type requires-Ethe use-of electrical energy, suchenergy may be transmitted toot-"from the :;down the borezholeto theturbine and todrive the turbine, eannenergydissipation device disposedabove and con- --nected;to;.said turbine,na core barrel including an outer srotatablebarrel. and a stationaryinner core receiving bar- ""Ii1idiSpOSd,b1OW; said turbine, said outer rotatable barrel adapted to be driven by.:said turbine, means to main- .tainzzthewhousing: of saidturbine in a stationary position 1 rotationally,-.a coringbitsecuredtothe lower end of said outer barrel and adapted, to be rotated. with said outer d i b ,meansofelectric'al cables, and the lik awhi h--aorpbarrehby said: turbine, andconduit means adapted to are run down the borehole. Hydraulic lines or other conduits forttransferringfluidsmay also be used as der sired. Indeed, it :is contemplated-although: not preferred-that the,:present apparatus may be used in' the v.direcL-the. gas exhaust from the turbine to the surface oft a: core :which ;is cut by said bit.

:6. -An apparatus asidefinedin claim 5 in which the :means tomaintain the housing of said turbine ina stapresence oforin conjunction-with a reduced level of 35.:iti0nary P rotationally 1'5 retractabledrilling liquid within a borehole. In this.instance,=fiexible tubing orother type conduitsmay be employed as neces .1 saw,

It'is further contemplated that the .apparatusof the in- 7. Inacoring operation wherein a bit is driven into a "formation underlying abore hole, the method of preservingEthecorewhich comprises maintaining a gas-driven -1-rnoto'r'=within;the: bore hole,;.supplying cool compressed .vention-while preferably employed ,in combinationwith" the-motoli-and thereby driving the motor, trails- .a' string of well pipemay alsobe employed in-a bore -hole which is devoid, of rigid piping. .In this case, the .retractable latching meansmay be adapted to engage or clamp against thev wall of .thebore hole itself; and a con- 1:v mitting;at least a portion of theenergy from the motor xiitorthe-bit and :thereby driving'the bit into the formation, dissipating 'at least a portionof the energy available from --:the-.motor,; directing the expanded exhaust gas from the duit, preferab1y in the. form of a Ramble-flexible gymotor against the; surface of the core as it is cut by the may: be usedto transmit gas down theborehole 'to'rdrive r. the turbine.

I: claim:

11..*A'fdrilling:apparatusadaptedtozbe used within the '-bit,,;- controlling .the total amount of 1 energy withdrawn fromdhe, motortso as to. cool the exhaust gas and chill the :core;:exhaustingthe. gasfromthe borehole after it has 2136611 directed against the core, parting the chilled core :lowermend'ofiastring of:.-w'ell pipe: which. comprises asfiOi-fromitheforma n; Withdrawing the core from the housing adapted .tobe supported from the -well pipe; a turbine mountedwithin said housing, an energy dissipa- .tion. device mounted. abovensaid turbine within saidhousing and adapted to be driven bysaid turbine, a core barrel positioned below. said housingandv supported from the shaft of said turbine, said core barrelincluding an-inner stationary barrel and anouter rotatingbarrel, a coring bitsupportedzatihe bottom .of. said outer barreL means for turning. said outer barrel responsive to movement of said turbine shaft, conduit meansradapted to convey fluid. 1 2,034,257

from-within said well pipe to said turbine, andmeansfor -matntaimng said housingin a. stationary rotational posi- -tion.

2., An:apparatus.asdefined .in claim l in which the housing, and core. barrel are adapted-to .passvertically within the well pipe, and the means for. maintaining the I housing in a stationary rotational position is'a retractable .latchingmeansladapted to engage and lock with recesses :zdisposed. within'the well pipe. I

.- bore hole.

1: 8.41. process asdefined in claim 7 in which the energy .rwhichzis-dissipatedfromthe.motor is dissipated at a point above, the 1 motor.

References Cited in the file ofthis patent UNITED STATES PATENTS 

